Your car doesn't have the A2DP bluetooth profile to stream audio.
Like the guy above said, it wasn't included in your production year.
You can buy a bluetooth receiver and plug it into your AUX port though. I use a blackberry stereo gateway and it is very good quality sound. The iPhone does a good job of integrating both the BT receiver and the BMW BT. It acts exactly like when you have headphones plugged into your iPhone. Music fades/pauses, call rings, when it ends, music resumes and fades back on.
Any BT receiver will work. Key word is RECEIVER not transmitter. Belkin makes one as well.